MONOCLINIC DOUBLE SULPHATES CONTAINING AMMONIUM. 
45 
Optic Axial Angles 2V a of the Copper Group. 
AmCu sulphate. 
KCu sulphate. 
RbCu sulphate. 
CsCu sulphate. 
Li. 
60 1 
o / 
46 1 
o / 
44 26 
o / 
43 6 
C. 
68 57 
46 6 
44 29 
43 9 
Na ..... . 
68 31 
46 32 
44 42 
43 24 
T1. 
67 40 
47 0 
44 57 
43 40 
F. 
66 55 
47 33 
45 15 
44 3 
Ammonium Cadmium Sulphate , (NH 4 ) 2 Cd (S0 4 ) 2 . 6ILO. 
This salt is not included in the investigations of Murmann and Hotter, but a few 
measurements of the crystals are given by Rammelsberg,* and these values are 
appended in the last column of the table of angles given on next page. All the forms 
given in the list of “ forms observed ” below were also observed by Rammelsberg. 
Crystal System. — Monoclinic. Class No. 5, holohedral-prismatic. 
Ratios of Axes .— 
a :b : c = 07364 : 1 : 0‘4931. Values of Rammelsberg, 07431 : 1 : 0‘4945. 
Axial Angle. — (3 = 106° 41'. Value of Rammelsberg, 107° 23'. 
Forms observed. — a{l00}, 6 {010}, c {001}, p {110}, p'{l20], jp w {l30}, q {Oil}, 
r'{20l}, o {111}, (/{Ill}. 
Habit. —Prismatic parallel to the axis c, sometimes fairly long as in fig. 11, but 
more frequently short and almost tabular parallel to c {001} as in fig. 12. 
* 
The crystals of this salt are exceptionally rich in faces, practically all the ten 
crystals measured exhibiting all the forms enumerated in the above list. They are less 
transparent than those of the other salts, being a translucent white. For this reason 
their optical investigation has presented considerable difficulty, and for the purpose of 
* ‘ Handb. der Ivrystall.-phys. Chemie,’ Leipzig, 1881, 1, 460. 
